Organic electroluminescence (hereinafter also referred to as “EL”) elements are known as light emitting elements which utilize an electroluminescence (EL) phenomenon. An organic EL element can emit light at colors of various wavelengths by selecting organic materials which form functional layers such as a light emitting layer, an electron injection layer and a hole injection layer, and applications for display devices and lighting equipment is progressing.
Both a low molecular organic material or high molecular organic material can be used as an organic material forming the functional layers described above. In particular, since a low molecular organic material has excellent thermal stability and is easy to handle, practical use as an organic material forming a functional layer of an organic EL device is already progressing.
Currently, vapor deposition of a deposition mask is mainly used as a method of forming an organic material forming each functional layer in an organic EL display device. A vapor deposition mask is a mask (shielding plate) formed by a metal foil (metal sheet) in which a plurality of fine slits or holes (hereinafter referred to as “opening parts”) are arranged at minute intervals, and is called a metal mask. For example, in the case of manufacturing an active matrix type organic EL display device, a vapor deposition mask in which a plurality of opening parts are arranged corresponding to the arrangement of a plurality of pixels (that is, regions where an organic material is formed) is used.
Normally, a vapor mask is fixed by welding or laser welding in a state where tension is applied to a strong rectangular frame. In addition, at the time of vapor deposition, a method of placing a vapor deposition mask on a substrate which is the object of vapor deposition in a state fixed to a frame and fixing and holding the vapor deposition mask from a rear surface of the substrate using a magnet or the like is generally adopted.
However, since the rigidity of a vapor deposition mask is extremely small, slight distortions may occur when the mask is held on the substrate surface, which may become a problem particularly in the manufacture of a high definition organic EL display device. In addition, the generation of metal foreign objects due to the contact between a vapor deposition mask formed by metal foil and the substrate surface has been regarded as a problem.
In view of the problem of rigidity described above, a method is proposed in Patent Document 1 and Patent Document 2 in which a resin such as polyimide is coated on a metal member forming a vapor deposition mask to form smaller opening parts in the resin located in the opening parts of the metal member. The effect of increasing rigidity by reinforcing a vapor deposition mask with resin was aimed for.